Preparation of mitotic chromosomes of leaf-cutting ants from the genera Atta and Acromyrmex

some modifications were made to the methodology of imai et al. (jpn. j. genet. 63: 159-185, 1988) for cytogenetic analysis of the leaf-cutting ants atta sexdens piriventris and acromyrmex heyeri (hymenoptera, formicidae), shortening preparation time and improving chromosomal preparations. the brain ganglia of prepupae were dissected in a 0.0025% hypotonic solution of colchicine, placed on a glass slide on a cold plate (4 ± 1oc) for 20 min. the material was fixed directly on the cold slide (with cold fixative i), macerated with a histological needle and fixed again with fixative i, followed by fixatives ii and iii, all of them cold. the slide was flame-dried right after the use of fixative iii, and it was allowed to air-dry at room temperature for 2 h. the resulting metaphases presented less contracted chromosomes, with separated and well defined sister chromatids at a high frequency, when the material was processed in the manner described and stained with 3% giemsa in phosphate buffer (ph 6.8) for 15 min.